Acids and Bases

This lecture serves as a transition into skills and clinical units.
The lecture content is not included in the case study assessment next week but will be in the final quiz.
The quiz opens midnight tonight and closes midnight Sunday, including questions on acids and bases.

Often referred to as the potential of hydrogen.
Focuses on understanding the behavior of hydrogen concentration.
Hydrogen (H) is element number one, with one proton in its nucleus and one electron.
A hydrogen ion (H+) loses its electron and becomes a proton.
- Very small element and is very important for the human body.
- Also seen in hydrocarbons.
Water (H2O) has two hydrogen atoms and one oxygen atom.
Covalent bonds between hydrogen and oxygen are strong but can break due to the constant movement of water molecules in liquid form.
When water molecules bump into each other, a hydrogen ion can break away, forming hydroxide (OH-). The electron remains with the Oxygen atom, and creates a negative charge.
Dissociation: Water molecule splits into hydroxide ion and hydrogen ion.
Hydrogen as a proton is quickly taken up by other molecules forming $H_3O^+$ , hydronium ion.
The reaction is reversible, reaching equilibrium in water.
Pure water has equal concentrations of hydrogen and hydroxide ions, resulting in a neutral pH of 7.
Solutes that are acids and bases in water disrupt this balance.

Measures a solution's acidity or alkalinity.
Arbitrary logarithmic scale from 0 to 14.
- 0 is most acidic.
- 14 is most basic or alkaline.
pH measures the amount of hydrogen ions in an aqueous solution in moles per liter.
Acidic solutions have more hydrogen ions (lower than 7 on the pH scale).
Alkaline solutions have more hydroxide ions (higher than 7 on the pH scale).
Logarithmic scale: each pH number change represents a tenfold change in hydrogen ion concentration.
- pH of 7 = $10^{-7}$ moles of hydrogen ions per liter.
- pH of 6 is 10 times greater concentration of hydrogen ions than pH of 7.
- pH of 2 = 0.01 moles per liter, 10,000 times stronger than pH of 6.

Solution with a pH of 5: hydrogen ion concentration is $10^{-5}$ .
A solution of pH 4 has 1,000 times greater hydrogen ion concentration than a solution of pH 7.
pH of 11 has a lower hydrogen ion concentration than a pH of 9.
Small pH adjustments can make significant differences due to the scale's exponential nature.
Hand soap is extremely alkaline (pH of 10), harsh on skin compared to skin's pH of 5.5 - 5.6.
Surfactant formulas (shampoos, body washes) are pH-balanced to be closer to skin's pH.
Exposure to water (pH 7) can cause dermatitis due to the difference in hydrogen ion concentration compared to skin.
Orange juice is a little bit more like our peel sort of pH, for example.

Inorganic acids, bases, and salts dissolve and dissociate into ions in water.
Water molecules form a hydration shell around the ions.
Acids: Substances that donate hydrogen ions to the solution when dissolved, increasing hydrogen ion concentration.
Referred to as proton donors.
Hydrogen ions attach to water molecules, forming hydronium ions.
Strong acids dissociate completely and irreversibly.
- Hydrochloric acid (HCl) dissociates fully into hydrogen ions and chloride ions.
- Sulfuric acid has solutions that have high concentrations of high hydrogen ions when it's placed into an aqueous solution or into water.
Weak acids, such as carbonic acid and acetic acid (ethanoic acid), can reform initial reactants and only partially dissociate.
Dissociation constant (pKa) measures the level of dissociation. Stronger acids have lower pKa values.

Lower pKa values indicate stronger acids, requiring more caution.
Higher pKa values indicate gentler acids with fewer complications.
Logarithmic scale ranging from 0.12 to 52.
Strong acids values are closer to zero
Weaker acids have values closer to nine
- Acids with pKa values less than 3 require extra caution.
Hydrochloric acid: pKa = 0.7
Acetic acid (vinegar): pKa = 4.75
Glycolic acid: pKa = 3.83
Lactic acid: pKa = 3.86
Pyruvic acid: pKa = 2.49
Trichloroacetic acid (TCA): pKa = 0.26 (very strong).

Reduce hydrogen ion concentration in a solution.
Two mechanisms:
- Directly accepting hydrogen ions.
- Increasing hydroxide ion concentration.
Some bases (e.g., ammonia) attract hydrogen ions, forming ammonium ions.
Other bases (e.g., sodium hydroxide) dissociate in solution, increasing hydroxide ion levels.
Reactions with two-directional arrows are weaker bases.
Unidirectional arrows indicate stronger bases like sodium hydroxide, which dissociates almost completely.

Mixing acids and bases can form salts and water.
Example: Hydrogen chloride and sodium hydroxide dissociate, then rearrange to form water and sodium chloride (table salt).
When hydrogen chloride and sodium hydroxide are added into water, the hydrogen and the chloride ions separate. In the case of sodium hydroxide, sodium and hydroxide ions separate out.
Then there's rearrangement and reforming of those.

Aqueous solutions containing a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid.
Keep pH at a specific range.
Internal buffering systems maintain narrow pH limits in the body.
Blood pH: 7.35 to 7.45 (slightly alkaline).
Saliva: Slightly alkaline.
Interstitial fluid: slightly alkaline.
Intracellular: Near neutral.
Gastric juices: Low pH of 1 to 3 (high hydrogen ion concentration for digestion).
Compatibility with life: pH ranges from 6.8 to 7.9.
Skin's acidic pH is a defense against microbes.
Respiratory and renal systems, along with circulating buffer systems, adjust pH levels.
Carbonic acid-bicarbonate buffer system: Carbonic acid (H2CO3) dissociates into hydrogen ions and carboxyl ions; bicarbonate molecule (HCO3) acts as a weak base.

Keep pH of a solution constant, ensuring stability.
Buffered peels are safer and easier to use.
Free acid peels require more caution.
Neutralization: Balancing an acid by adding an alkaline substance to reach a pH of 7.
Lactic acid can be neutralized by sodium bicarbonate solution.
Sodium bicarbonate solution is used to remove those extra hydrogen ions.
Self-neutralizing peels: Salicylic acid (BHA), trichloroacetic acid, Jessner peels, phenol peels; excess is removed, rather than neutralizing the peels.
Water is enough to remove the excess of the peels.
Alpha hydroxy acid peels need to be neutralized at the end of the procedure. Neutralizing Solution
- Is needed as a safety precaution measures in case of frosting in the skin due to damage to skin tissues.
Partially neutralized peels: Acid mixed with a small amount of base, leading to a gradual release of free acid.
Gives more control to this process, and makes the product safer.